Throughout this application various publications are referenced by the names of the authors and the year of publication within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
This invention relates to the rapid development of plant varieties resistant to certain types of cost-effective herbicides. It includes the production of new crop varieties resistant to such herbicides including potatoes and certain Solanaceous crops, as well as other crops produced asexually or through seeds. The invention is limited only by the compatability of the cytoplasms from a resistant species with the nucleus and other cellular components of the crop in question.
Certain weed species that were under intensive selection pressure in the field, have evolved resistance to the chloro -s -triazine group of herbicides (cf. LeBaron and Gressel, 1982). This resistance could be useful in areas where this group of herbicides has not been over-used, and with crops that need a good broadspectrum herbicide with sufficient soil residual activity as to give season long control of weeds in that crop. Genetic experiments have shown that this triazine resistance in weeds is often maternally inherited (cf. Souza-Machado, 1982), and biochemical evidence suggests that this trait is inherited in such cases on the DNA of the chloroplasts. Thus, it is necessary to transfer only chloroplasts to a crop in order to confer resistance. The first case of possible maternal inheritance of triazine resistance was found in Brassica campestris (cf. Souza-Machado, 1982). Just after this was found, it was suggested that this trait be somehow transferred to the crop Brassica napus (rape seed) using the new procedures of protoplast fusion (Gressel et al, 1978). Despite this suggestion, scientists transferred triazine resistance by crossing the two species, and backcrossing to B. napus until a new variety was ready (cf. Souza-Machado, 1982), a process requiring more than 5 years of crosses and back-crosses. The methodology of cybridization (transferring of only cytoplasmic genomes without the nuclear genome, by protoplast fusion) had only been worked out in sufficient detail for Nicotiana (Zelcer et al, 1978) and in a few other cases. Real successes with this methodology was not achieved with crops, even though there are many resistant-weed; susceptible-crop pairs with sufficient relatedness to expect that such a transfer could be successfully accomplished (Gressel et al, 1982). Indeed, previous attempts using the methods of Zelcer et al. (1978) were only able to perform fusions which contained the nuclei of triazine-resistant Solanum nigrum (Black Nightshade) as well as nuclei S. tuberosum (potato). The fusion products segregated, as expected to plantlets which are triazine resistant and plantlets which were susceptible to triazine. (Binding et al, 1983). Of the more then 2000 plants tested, only one resembled S. nigrum; but it was triazine susceptible and contained chloroplasts which were biochemically determined to be those of potato (Gressel et el, 1982). This showed that spontaneous cybridizations could occur, but this would not be a practical method. This also showed compatibility between nightshade nuclei and potato chloroplasts, although the reverse need not have necessarily been so.
The methods of this invention can also be used to transfer maternally inherited resistance to other herbicides. (cf. Gressel, 1985). Such resistance would be easier to transfer from variety to variety by means of directed photoplast fusion of this invention. Other cytoplasmically inherited traits can be transferred using the same methodologies.